1. Field of the Invention
This invention relates to an apparatus and method for thawing materials carried in containers such as gondola rail cars, trucks and the like, and more particularly to such an apparatus and method employing microwave heating techniques during the thawing operation.
2. Description of the Prior Art
Many natural and man-made materials are most economically transported in broken or granular form by open rail cars. These rail cars collect moisture due to rain, high relative humidity, and the like. In cold or freezing weather below zero degrees celcius these materials often become frozen, and discharge thereof either from the bottom the cars or by various tipping or rotary dumping methods becomes difficult or impossible.
Various thawing methods and apparatus have been proposed in the Prior Art. Early thawing efforts described in U.S. Pat. No. 2,507,775 included the building of wood fires under the cars, the holding of gas jets against the sides of the cars in various places, and the use of steam baths to which parts of the car or the whole car were subjected. These methods have, however, proven unacceptable since they either subject the rail car to excessive localized temperatures which can cause buckling or other serious structural weakening of the car, distruction of the paint on the car, and/or inpart insufficient heat to the car and its contents to insure thorough thawing of the material contained therein.
Modern attempts at providing economic and efficient railway car thawing systems have utilized electrical energy heating devices to fullfill the thawing function. Thus, as is disclosed in U.S. Pat. No. 3,569,657 microwave energy is emitted through an access opening provided in the bed of a transport vehicle such as a truck trailer of a railway vehicle car, with the transport vehicle then serving as a microwave cavity for heating the contents thereof. However, this microwave heating system would appear to find utility only with special purpose vehicles specifically provided with microwave access openings, with the vehicles being closed to provide the requisite microwave cavity. Thus, in order to implement this system on a large scale, a massive capital expenditure would be required of the railroad industry to refurbish existing rail coal cars and the like.
Yet another modern railway car thawing system disclosed in U.S. Pat. No. 3,800,858 achieves thawing by heating the sidewalls and bottom of the railcar, and the exposed upper surface of particular matter contained therein, by means of infra-red generating heaters suitably positioned to radiate heat to the various surfaces. However, this technique again relys on heating of the vehicular container and thus therefore suffers to some extent for the same reasons as discussed above.